Telephone-exchange system



F. LUBBERGER AND W. PINELL.

TELEPHONE EXCHANGE SYSTEM.

APPLlCATiON FILED SEPT. 20.1915 7 7 193999669 Patented Dec. 6, 1921..

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TELEPHONE EXCHANGE SYSTEM.

APPLiCATlON FILED SEPT. 20. 1915.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED SEPT. 20, 1915.

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APPLICATION FILED SEPT. 20, 1915.

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APPLICATlON FILED SEPT. 20,1915.

Patented Dec 6 1921,

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TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED SEPT. 20, 1915.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED SEPT. 20 1915.

Patented Dec. 6, 1921,

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-FRITZ LUBBERG-EB, OF BEIRLIN-HAIJENSEE, AND WALTER PINELL, OF SIEIWENSSTADT, N BERLIN, GERMANY, ASSIGNORS, BY MES'NE ASSIGNMENTS, vTO WESTERN ELECTRIC COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

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Specification of Letters Patent.

Patented Dec. 6, rear.

To allwhom it may concern:

Be it known that we, FRITZ LUBBERGER and WALTER PINELL, citizens of the German Empire, residing, respectively, at Berlin-Halensee, Joachim Friedrich 41, and Siemensstadt, near Berlin, Brunnenstr. 15, Germany, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to overflow trunking systems for telephone exchanges.

Tn telephone systems there is a daily period of time durin which the trafiic is abnormally large. imilar periodical increases in the traffic are observed at Christmas or on special occasions. In view of the fact that the duration of these jumps in the traflic does not exceed a few days in a whole year, it would not be justified, for economical reasons, to enlarge the telephone exchange with a view to handling the exceptional trafiic. The apparatus that must be provided for handling the estimated periodical traffic overflow could not be eiiiciently utilized.

It is the object of the present invention to provide an economical arrangement for telephone exchanges to handle such excessive traffic.

According to one feature of this invention, in addition to the trunks that may be reached in response to the setting of the selector switches, auxiliary trunking means is provided in common to a plurality or all the groups of trunks. The auxiliary trunking means may comprise a plurality of auxiliary trunks, one of which may be seized by a selector if it encounters only busy trunks in the desired group. One and the same auxiliary trunk may be seized by a selector upon the unsuccessful testing of any one of a plurality of trunk-groups, and for this reason the identity or direction of a connection would be lost upon the seizing of an auxiliary trunk. According to the present invention, means are provided for identifying the direction of a connection upon its extension to an auxiliary trunk, whereby a calling incoming line may be extended through one and the same auxiliary trunk to any one of 'a plurality of groups of outgoing lines or trunks. I i

According to another feature of this invention, an auxiliary switching device is associated with each auxiliary trunk. The auxiliary switching device is first set in accordance with the numerical designation of the group that was unsuccessfully hunted over by the selector through which the connection was extended to the auxiliary trunk.

'The set of impulses, by means of which the setting of the second group selector (the one beyond the last mentioned selector) was intended, will cause the auxiliary switching device to perform a second operation in response to these two operations of the auxiliary switching device, the calling incoming line is extended through the last mentioned device, to a trunk which, under normal traffic conditions, would have been seized by the second group selector.

. Supposing that all the trunks of a desired group of outgoing trunks, for instance, the group comprising trunks Nos. 20,000 to 29,999, are held through a certain group of incoming trunks or lines. Under these circumstances it.-is highly improbable that all the incoming trunks are connected to one and the same subgroup of outgoin trunks (for instance, the No. 28,000). l robably some of the outgoing trunks of thegroup No. 28,000 are idle. By means of the mentioned auxiliary switching. device, a calling incoming line desiring connection with a trunkbelonging to the subgroup No. 28,000, will be connected thereto through an auxiliary trunk, while all the incoming trunks, through which under normal traffic conditions access may be had to this subgroup, are busy.

The auxiliary switching device may comprise a plurality of auxiliary selectors or a single auxiliary selector. In the latter case, the auxiliary selector is operated in the same manner as a connector, 2'. 6., it is first set onto a group of terminals corresponding to a group onto which the setting of the first group selector was desired, and then it is set onto a special set of terminals corresponding to the terminals onto which, under thus the establishment of a desired con-- nection is insured.

If one-movement selector switches, for instance, selector switches that move only in a vertical direction, are used, means are provided whereby, in case all the regular trunks are busy and the selector moves onto the terminals of an auxiliary trunk, the terminals located between the desired trunk terminals and the auxiliary trunk terminals will not be tested. As well known, selector switches of this type are provided with two banks of test contacts, and in accordance with the present invention, the testing of the auxiliary trunks is effected through the bank through which the group testing is effected. "When all the regular trunks are found busy, a change-over operation is effected under the control of current impulses of a certain duration or strength, whereby the-testing will be controlled in the other bank of test contacts.

If two-movement switches, such as, for instance, switches of the well-known Strowger type, are utilized, the switch is moved onto the terminals of an auxiliary trunk.

if all the trunks of the desired group are found busy, the auxiliary trunk terminals being provided in the top row of the terminal bank.

After the setting of a group selector switch, 6. 9., the first group selector, onto the terminals of an auxiliary trunk, it is necessary to repeat the impulses by means of which the group selector switch was set onto the desired group of regular trunk terminals. For this purpose means may be provided to send a signal to the calling subscriber, indicating to him that he hasto repeat the sending of a series of impulses. The provision of such means is, however, not desirable, and another feature of the present invention contemplates the arrangement of a register equipped to send out a series of impulses any desired number of times. -The register comprises impulse receiving means for storing up the impulses sent from a telephone substation or an operators position, and impulse transmitting mechanism for sending the impulses toward the various selector switches. The impulse transmitting mechanism of the register is successively operated to send out the various series of impulses that compose the number of the called subscriber. Obviously, however, impulse controlling and registerin mechanisms of other types may be use without departing from the spirit of the present invention. The change-over operation whereby the successive sending out of the impulse series is effected, occurs under the control of the selector switches. If a selector is set onto the terminals of an auxiliary trunk and it becomes necessary to repeat a series of impulses, the change-over operation is delayed. Depending on the capacity of the exchange, the register may thus be controlled to repeat a plurality of series of impulses. i

The present invention may be advantageously embodied in systems in which long distance and toll traffic is handled. Usually, only a limited number of toll or district selectors are provided for each group of trunk lines. In order to accelerate the establishment of toll connections, according to another feature of this invention, a toll or district selector switch that could not find an idle long distance trunk is set onto the terminals of trunks that are ordinarily used for establishing only local connections. This local trunk is utilized now as an auxiliary trunk in the same manner as above deparatus may be provided at the intermediate switching mechanisms.

This invention may be utilized in systems in which separate, connecting and talking circuits are established during the building up of a connection. Hall the talking conductors which may be used are busy, talking conductors that are normally used in local connections may be transformed for toll service. In such arrangements there is provided a switching center for producing three different operations. In response to one operation of the switching'center a connecting circuit is seized, in response to a second operation a local talking circuit is seized, and in response to a third operation a toll talking circuit is seized. In the drawings, Figures 1, 2, 5, 6 and 7 are schematic representations of the various i,see,oce

3, 3, 3 and 3 show the circuit diagrams of t with Figs. 5 and 6.

a telephone exchange system schematically represented in Fig. 1; Figs. 4 and 4 represent the circuit diagrams of a telephone exchange system schematically indicated in Fig. 2; and .Fig. 8 represents the circuit diagram of a telephone exchange system schematically indicated in Fig. 7. The operation of the circuits necessary to operate the systems schematically indicated in Figs. 5 and 6, is not disclosed in detail. In view of the circuits disclosed in Figs. 3 to 3 and the systems disclosed in the French patent No, 462,306, one skilled in the art will be able to furnish the detailed circuit arrangement for operating a system in accordance According to the arrangement shown in. Fig. 1, the calling substation 1 may be connected by means of a line finder 2 with an idle first group selector 3. A finder switch 4 is operated thereupon to connect a register Reg to the first group selector. At the first group selector there is provided after the last group of trunk terminals a group XI in which the auxiliary trunks terminate. If a connection is desired through a trunk belonging to group II and all the trunks of this group are busy, the first group selector 3 moves automatically to a free auxiliary trunk 5 and renders this trunk busy. Under the control of impulses repeated by the register, an auxiliary selector 6 is set on to terminal TI corresponding in numerical designation to the terminals of the trunks of group H. No trunk hunting means are provided for this auxiliary selector, but after being set it extends the calling incoming line to another auxiliary selector 7 which is set in the same manner as a second group selector 8. This latter auxiliary selector is arranged to hunt for an idle trunk in the selected group and establish va connection through. a connector 9, with a called. substation 10.

In accordance with the arrangement shown in Fig. 2 an auxiliary selector 12 may be operated in accordance with two series of impulses, the one destined for setting the selector 3 and the other destined for setting the selector 8. The terminals of this auxiliary selector are not multipled and no trunk hunting means are provided in association therewith. After the setting of the auxiliary selector switch, an intermediate selecting apparatus 13-14 is operated. The intermedisent more in detail the circuit arrangement of a telephone exchange system arranged 1n accordance with Fig. 1. The selector swltches employed may be of the type disclosed in the patent to Grabe No. 1,343,714,- issued June 15, 1920.

The operation of this system is as follows:

The calling substation 1 is' connected in' the well-known manner by means of line finder 2 to the idle first group selector 3. Upon the extension of the calling line by the line finder, relays 16 and 17 associated with the first group selector, and the line finder, respectively, become energized, the circuit being closed through a normally closed contact 200 of the first group selector, and the test wiper of the line finder 2. Relay 17 doses, through its front contacts an energizing circuit for relay20. Relay 2O closes through its contact 21 a circuit for a slow to release relay 22 which, by closing its contact 23, established an energizing circuit for a magnet 24. By closing its contact 23 the relay 22 connects round to the windings of relays 16 and 1%, and provides thus an energizin path for these relays independently of t e contact 200. Relay 22 closes in its contact 25 a circuit for a testing magnet 26 of the first group selector 3, from grounded battery through the winding of test magnet 26, contact 25 of relay 22, contact 27 of relay 28, and contact 29 (closed as long as the first group selector remains in its normal position) to ground. Relay 16 establishes a circuit from grounded battery through the left-hand winding of a relay 32 (Fig. 3

the winding of relay 33, a resistance 33', con ductor 16, the back contact and armature of a relay 35, and the front contact and armature of relay 16 to ground. Upon the energization and armature of relay 41 to ground. Relay 36 by closing its contact 42 establishes a locking circult for itself, and by closing: its contact 43 establishes a circuit from grounded battery, through an interrupter 19, the winding of driving magnet 44,- contact 45 of relay 41, and contact 43 of relay 36 to ground. Furthermore, relay 36 closes a circuit from grounded battery, through the right-hand winding of relay 32, the armature and front contact of relay 33, contact 210 of relay 36, and contact 217 of relay 41 to ground.

Under the control of magnet 44 finder switch 4 (Fig. 3 is caused to hunt for the first group selector 3. Upon the seizure of a trunk leading to the apparatus associated with the first group selector 3, a circuit is established from grounded battery through the windings of relay 41, contact 30 of, relay 36, wiper T of finder switch 4, conductor 211, contact 37 of relay 22, the winding of relay 35, and wiper 49 of a side switch associated with the first group selector, to ground.

By opening its contact 45, relay 41 causes the denergization of magnet 44, whereupon the finder 4 is arrested in its movement. In its contact 221, relay 41 establishes an enerizing circuit for slow to release relay 220.

pon the energization of relay 220 the energizing circuit of relay 36 is opened, and in view of the fact that the holding circuit of this relay is open in contact 40 of relay 41, it becomes deenergized. Relay 41 locks up throu h its left-hand winding and contact 50. K circuit is closed for relay 51 from grounded battery through the winding of this relay, contact 52 of relay 41, wiper II of the finder 4, conductor 212, the upper front contact of relay 20, contact 53 of relay 22, and a resistance 54 to ground. Upon energization, relay 51 closes its contact 55, whereupon a slow to release relay 56 becomes energized. In response to current impulses (interruptions of the line circuit) sent out from the substation 1, relay 20 and therefore relay 51 are intermittently de'nergized and energized. Upon its first deenergization, relay 51 closes a circuit for a slow to release relay 57 from grounded battery through the winding of this relay, contacts 58 and 59 of relays 56 and 51, respectively, to ground. Upon the energization of relay 57 and the closure of its front contact, a.

side-switch magnet 60 becomes energized. Under the control of these relays, a driving magnet 63 associated with the thousands impulse receiving register 61 is intermittently energized and denergized. The current interruptions are not of a sufliciently long duration to permit the deenergization of relays 56 and 57. Depending on the number of impulses sent out from the substation, the thousands impulse receiving register 61 is moved into a certain position. After a series of impulses have been sent out, the line circuit is closed for a relatively longer period, whereupon relays 20 and 51 become permanently energized. By opening its contact 59, relay '51 causes the deenergization of relay 5'7. Relay 57 opens the circuit of side switch magnet 60. Upon the deenergization of magnet 60 a wiper 62 of a side switch is moved into its second position, whereupon the circuit of the driving magnet 63 of the thousands impulse receiving register is opened, and a circuit is closed for a driving magnet 64 of the hundreds impulse receiving register 65. Each impulse receiving register is provided with a releasing magnet 66 to 69. These magnets are energized upon the energization of relays 56 and 41. When the finder 4 is released and relays 41 and 56 become deenergized, these release magnets become also denergized and restore the registers to normal.

The sending out of impulses from the registering mechanism may be started immediately upon the setting of the thousands impulse receiving register. The side-switch wiper 62 is now in its second position and a circuit is established from grounded battery through an off-normal contact 70 of the thousands impulse receiving register, a side switch wiper 71, the winding of relay 72, wiper IV of finder 4, conductor 215, side switch wiper 73 of the side switch associated with the group selector 3 (in position 1), front contact and armature of magnet 26, and contact 74 of relay 75 to ground. Relay 72 closes a circuit from grounded battery through interrupter 76, the back contact and armature of relay 77 the winding of driving magnet 78 of the impulse sending register 31 and contact 79 of relay 72 to ground. Magnet 78 by intermittently closing and opening its right hand front contact causes the intermittent energization and deenergization of relay 28 associated with the first group selector 3, the circuit being closed from grounded battery, through the front contact and armature of relay 78, finder wiper III, conductor 213 and the winding of relay 28 to ground.

Upon the first energization of relay 28, the circuit, which was closed through test magnet 26, contact 25 of relay 22, contact 27 of relay 28, and the normally closed off normal contact 29, is opened and since, upon the energization of relay 22 the release magnet 24 was energized over a circuit through contact 23 of relay 22, the power driven shaft of the selector is permitted to advance until the test wiper 81 engages terminal 00. Relay 22 upon energizing closes a circuit for slow to release relay 80 which prepares a circuit for magnet 26 for arresting the wiper 81 on terminal 00. The circuit of magnet 26 may now be traced from grounded battery, through magnet 26, the left hand front contact of relay 80, test wiper 81 of the first group selector, terminal 00, the left hand inner front contact and armature of relay 28, and contact 82 of relay 75 to ground. Assuming that in the present case two impulses are sent out by the register, the callingsubscriber desiring a connection to a subscriber whose line may be reached through a trunk of the second group, the circuit of magnet 26 is opened upon the first deenergization of relay 28, and the group selector is moved another step, its test wiper 81 engaging terminal 000. Magnet 26 is now. energized over a circuit extending through the front contact of relay 80, wiper 81, terminal 000, back contact and inner left hand armature of relay 28 to ground at contact 82 of relay 7 5. Upon the second energization of relay 28, the circuit of magnet 26 is again opened and the switch wipers are permitted to advance over all of the terminals of the first group, until test wiper 81 engages the last contact of the first group,

wipers. When relay 28- deenergizes for the second impulse, magnet 26 again releases the wipers and arrests them after they haveadvanced one step. As no further impulses are sent, the slow to release relay 80 becomes denergized and opensat its left hand front contact the circuit of magnet 26, causing the selector to advance another step to position the test wiper 83 upon the first terminal of the selected second group. At its-left hand back contact, relay 80 prepares a circuit from wiper 83 of the group selector 3, through the left hand winding ofpolarized relay 75, contact 84 of relay 22, contact 85 of relay 75, the winding of polarized relay 86, the lefthand back contact and armature of relay 80 and the winding of magnet 26 to grounded battery.

. As soon as the contact to which the thousands impulse receiving register 61 applied ground is found by the thousands impulse sending register, relay 77 becomes energized. The circuit of this relay is closed from grounded battery, through its winding, the inner right hand front contact and armature of relay 72, side switch wiper 87, the wipers of the thousands impulse sending and receiving registers to ground. Upon the energization of relay 77, its right hand back contact is opened, whereupon magnet 78 becomes energized.

If there is an idle trunk available in the desired group theconnection is established over the second group selector 8, 3". If, however, all the trunks in the selected group are busy, the first group selector-is set on to an auxiliary trunk for establishing the desired connection.

As long as busy terminals are engaged, such terminals being supplied with reduced potential, the test "magnet 26 of the group selector will not receive sufficient current -to ener ize to arrest the advance of the switch wipers.

When the test wiper 83 contacts with the terminals of an idle trunk, however. a circuit is closed from grounded battery through the winding of test magnet 26, the left hand armature and back contact of relay 80, the winding of polarized relay 86, contacts 85 and 84 of relays 75 and 22 respectively, the left hand winding of polarized relay 75, test wiper 83, the right hand Winding and contact 88 of relay 89 (Fig. 3") to ground. Relays 86 and 89 and the test magnet 26 become energized. The polarized relay 75 remains denergized since the current fiowin in the test circuit is not of the right polarity to energize this relay. Upon the energization of relay 86, relay 95 associated with the register becomes energized, the circuit being closed from grounded battery, through off normal contact 96 of the side switch associated-with the registers, the winding of relay 95, wiper VI of the finder 4, conductor 216, wiper 97 of the side switch of the group selector 3 (in position 1), and contacts- 98 and 99 of relays 86 and 75 respectively to ground. Upon the energization of relay 95, the side switch magnet 100 associated with the sending register 31 becomes energized and causes the movement of the side switch wiper 87 to the next position in which the impulse sending register is controlled in its movement over wiper 65 of the hundreds receiving register.

Relay 86 also closes a circuit for magnet 90 controlling the side switch associated with the first group selector 3. The circuit extends from grounded battery through the winding of magnet 90, side switch wiper 94, contact 230 o relay 86, and interrupter 231 to ground. Upon the energization. of,

cuit being closed from grounded battery,

through the resistance 103, (Fig. 3 the lower back contact and armature of relay 104, trunk conductor 105, selector wiper 106, side-switch wiper 101, and the winding'of relay 102, to ground. Relay 102 closes in its left-hand (outer) front contact, a circuit from ground, through side-switch wiper 73, conductor 215, the wiper IV of the finder 4, the winding of relay 72, side-switch wiper Z1 and off-normal contact 70, 'to grounded battery. Relay 72 closes a circuit for driving magnet 78 and this magnet causes the sending of the hundreds impulses. Under the control of. contact 107 of relay 28,

a relay 108 (Fig. 3") associated with the.

the seizure of this trunk by other selectors,

as due to the increased resistance the test .magnets of other group selectors attempting to seize the trunk, cannot become energized.

Upon the energization of relay 89, release m'agnet 109 and test magnet 104 become energized. The energizing circuits extend from grounded battery through the "winding of magnet 109 and contact 235 of relay 89 to ground; and from grounded battery, through the winding of relay 104, normally closed contact 112 of selector 8, and the left-hand front contacts and armatures of relays 89 and 108 to ground. As soon as relay 108 receives the first impulse, it opens the circuit of relay 104 permitting the selector to advance its wipers to terminal 00, and closes an energizing circuit for a slow to release relay 110. Relay 110 becomes energized and disconnects in its back contact the test relay 104 from test wiper 113. A new circuit is now closed for relay 104 extending from ground through the right hand outer armature and front contact of relay 108, terminal 00, test wiper 111 of the second group selector 8, the front contact and armature of relay 110, and the winding of relay 104 to grounded battery.

'After the sending out of the first impulse and upon the subsequent de'e'nergization of relay 108, relay 104 denergizes and the wipers of the second group selector 8 are set to terminal 000. Upon the termination of the transmission of impulses, the relay 108 causes the denergization of relay 110. Upon the deenergization of relay 110, the test relay 104 is disconnected from test wiper 111, and is connected to test wiper 113. lVhen a trunk leading to a free connector 9 is sized, test relay 104 and relay 114 (associated with the connector 9 Fig. 3) become energized the circuit extending from grounded battery, through the winding of relay 104, the armature and back contact of relay 110, contact 135 of relay 89, wiper 113, the lefthand windings and contact 115 of relay 114 to ground. Upon the energization of relay 104, the second group selector 8 is arrested and the talking conductors are extended to the connector through the front contacts of this relay. The relay 114 connects through its contact 115 the high resistance winding in series with the low resistance winding for rendering this trunk inaccessible to other second group selectors.

Upon the energization or relay 104, the relay 102 is momentarily de'e'nergized, and by opening its left-hand (inner) front contact causes the de'energization of relay 95, whereupon the side switch associated with the sendin register is stepped into position 3. Upon the termination of the sending out of impulses, the slow to release relay 80 becomes deenergized, its circuit being opened at the right hand outer front contact of relay 28. Relay 80 opens at its right hand front contact the circuit of magnet 90, whereupon the side switch associated with the first group selector 3 is moved into posi tion 4.

The sending out of the tens and units impulses now follows. After the setting of the group selector 8 on to an idle trunk relay 102 again becomes energized, battery being supplied to its windings through the lower back contact relay 116 (Fig. 3.) Upon the first energization of relay 28 a circuit is closed from ground, through contact 107, side switch wiper 240, selector wiper 241 of selector 3, conductor 242, the upper armature and front contact of relay 104, Wiper 243 of selector 8, conductor 244, the upper armature and back contact of relay 116 and the winding of relay 117 to grounded battery. Relay 117 becomes energized, and opens the circuit of test magnet 121, which circuit was closed upon the energization of relay 114, and extends from battery, through the normally closed off normal contact 300, left hand winding of magnet 121, the off normal contact 301, left hand armature and to advance to terminal 000. In this manner the switch is advanced in response to the tens impulses. Relay 118 remains energized during the sending out of the tens impulses which is accomplished by operating relay 117 through the agency of relay 28. After the sending out of the tens impulses, the side witch associated with the first group selector is moved into its fifth position, whereupon the units impulses are sent out. After the sending out of the tens impulses, relays 117 and 118 become denergized, whereupon relay 119 becomes energized, its circuit being completed through the off normal contact 120 of connector switch 9. Relay 119 closes a locking circuit for itself extending from grounded battery, the winding of relay 119, contact 120, the lefthand front contact of relay- 1'19 and the outer right hand armature of relay 114 to ground. Upon the de'e'nergization of relay 117, slow to re lease relay 122 becomes energized over a circuit extending through the right hand middle armature of relay 114 and closes a circuit from grounded battery, through its contact 245, the left-hand winding of adifferentially wound test magnet 121, contact 246 of relay 122 and contact 248 of relay 119, to ground. Relay 119 prepares a circuit over its inner right-hand armature and front contact including the right-hand winding of the test magnet 121 and the Winding of an auxiliary magnet 123.

Upon the energization of relay 117, the right-hand winding of magnet 121 and the winding of auxiliary magnet 123 become energized. If both windings of differential magnet 121 are traversed by current. the magnet. will not pull up. Magnet 123 being now energized the connector is moved by half a step. After the sending out. of the impulse, the circuit of test magnet 121 and the auxiliary magnet 123 is interrupted. whereupon magnet 121 will again attract its armature, causing the selector to complete a test relay 116, contact 247 I, of relay 122,.

the right-hand back contact 'and armature of relay 118, the right-hand (outer) armature and front contact of relay 119, a group testing wiper 124, and the winding of relay .125 to ground. Relay 116 closes, through contact 126, a locking circuit for itself.-

After the whole set of impulses has been sent out, side-switch wiper 101 (Fig. 3) is in position 6. Relays 35 (Fig. 3) and 41 (Fig. 3 become deenergized. Upon the deenergization of relay 41, its contact 127 is closed and a release magnet 128 of the impulse sending register is energized for restoring this register to normal, the energizingcircuit of this magnet being maintained closed over off-normal contact 129 and contact 127 of relay 41. The deenergization of relay 41 also causes the deenergization' of release magnets 66 to, 69 for releasing the impulse receiving register. In position 6 of the side switch, ringing relay 130 (Fig. 3) is connected in circuit with an interrupter 131 and causes the application of ringing current to the called subscribers line. As soon as the receiver at the called. sta tion 10' is removed from the switchhook, a relay 132 (Fig. 3) becomes energized and closes a circuit for relay 18, from grounded battery, through the winding of this relay contact 250' of rela 132 andcontact 21 of relay 20 to groun Relay 18 is operated for the purpose of putting the restoration of the first and second group selectors and the connector under the control of the called subscriber. The relay 18 remains locked up until the selector 3 opens its off-normal con tact 251. Upon the restoration of the receiver at the calling substation, relay 20 becomes deenergized. Under the control of this relay, only the switch 2 is restored to normal. i

When thecalled subscriber restores his receiver, relay 132 becomes deenergized and causes the denergization of relay 22, relay 89 and magnet 26 and selector '3 is thereupon returned to normal under the control of release magnet 24, Magnet 24 becomes deenergized and locks the group selector in its normal position. The circuit of release relay 18 is interrupted at contact 251. Due to the closure of contact 200, ground is connected to the test wiper of line finder 2 over relay 16, so that the first roup selector 3 is now marked as free. pon the deenergization of relay 89, contact 135 is opened, whereupon the relay 104, associated with the second group selector, becomes deenergized. This selector 8 is then returned to its normal position. in which position the circuit of relay 104 is opened. The restoration of connector 9 is effected in a similar manner.

If no free trunk is available in the desired group, the first group selector 3 is moved with its wipers to the terminals of a so called overflowor auxiliary trunk. The

plus'pole ofa battery 136 is connected tov the test terminal of this trunk. Due to the fact that the resistance 137, included in the test circuit, prevents the energization of test magnet 26, only relay becomesenergized. Relay '75 closes a locking circuit for itself through contact 138 and connects magnet 26 and relay 86 through contact 139, to the group testing wiper 81. Upon the opening of contact 82 of relay 75, the ground is disconnected from the group test contacts, and, due totheclosure of contact 140 of this relay, a relay 141, associated with the register, becomes energized. The circuit of relay 141 extends from grounded battery, through an off-normal contact 260, the winding of relay 141, wiper V of finder 4, conductor 214,

contact 140 of relay 75, and contact 142 of relay 86 to ground. Relay 141 closes in its lay and the'test magnet 26 being connected to the terminal bank through which the groups are tested, and since ground has been removed at contact 82 of relay 75 from all regular group contacts the selector is moved over the terminals of all the regular trunks. The auxiliary trunks are tested on the terminal bank serving for group testing. As soon as the wiper 81 contacts with the test terminal P of an idle auxiliary trunk, relays 86 and 26 become energized. Relay 86 causes the stepping of the side switch in position 2 as previously described. The side switch, however, cannot be stepped into its third position, the interrupter 92 being disconnected at contact 91 of relay 75. Upon the energization of relay 86, contact 142 is opened, whereupon relay 141 becomes, deenergized. Due to the fact that relay 75 is already energized when relay 86 pulls up its armatures, i. 6., contact 99 is opened before contact 93 is closed, the relay 95 cannot become energized in position 1 of side switch 90. The ener ization of the side-switch magnet an the change-over for sending out the hundreds impulses are thus delayed.

auxiliary trunk becomes energized as follows: grounded battery, the winding of magnet 26, back contact and left hand armature of relay 80, test relay 86. the armature and contact 139 of relay 75, test wiper 81, contact P and connects its high resistance winding in circuit for rendering the selected trunk busy. Relay 102 associated with the first group selector becomes energized by IOU Relay 143 associated with the seized free current flowing through a circuit including the lower armature of relay 147 and wiper 106 and side switch wiper 101 of selector 3. Due to the closure of the left-hand (outer) front contact of relay 102, relay 72 is connected in circuit over side switch wiper 73. Side-switch wiper 87 being still in position 1, the series of impulses which were sent to the first group selector are sent out again. The impulses cause the setting of auxiliary selector 7.

This auxiliary selector 7 is not provided with means for automatically hunting for idle trunks. A rotary driving magnet 144 and a slow to release relay 145 are connected in series to the trunk conductor 146 and in response to the sending out of impulses the driving. magnet 144 is operated. In order to prevent false testing, while the switch is in movement, the relay 145 disconnects the test magnet 147 from the test wiper 148.

The auxiliary selector 7 is of the same structure as the second group selector 8, relay 149, but, does not connect a high resistance winding to the test conductor. -Upon the energization of relay 149, circuits are established for magnets 150 and 151. These circuits extend from grounded battery, through release magnet 150 and contact 270 of relay 149; and from grounded battery, through the winding of magnet 151, nor mally closed contact 271 of selector 7 and the left-hand armatures and front contacts of relays 149and 152 to ground. Upon the receipt of the first impulse by relay 152, a slow to release relay 153 becomes energized andthe magnet 151 becomes deenergized to advance the switch wipers to terminal 00. A new circuit is now closed for magnet 151 through the front contact of relay 153, and due to the closure of the right-hand (outer) front contact of relay 152, ground is connected to terminal 00' of selector 7.- The auxiliary selector 7 will be arrested on thls terminal, test magnet 151 being energized.

' After the sending out of the impulse and the deenergization of relay 152 the auxiliary selector 7 is moved to terminal 000. If no further impulses are sent out relay 153 becomes deenergized, its circuit being opened in the right-hand (inner) front contact of relay 152. Due to the actuation of the armature of relay 153, the test magnet 151 is disconnected from the group testing brush, and connected to the units testing brush. Upon the seizure of an idle trunk leading jto a free connector 9, test magnet 151 and relay 114 associated with the connector become energized. The auxiliary selector 7 is arrested and the talking conductors L L are extended over the front contacts of magnet 151 and the wipers of selector 7. At the same time the contact 115 (Fig. 3) is closed and the high resistance winding of relay 114 is connected in circuit. The setting of the connector 9 and the release of the switches are performed in the same manner as above described.

Figs. 4 and 4 represent a circuit arrangement in which a single auxiliary selector 12 and intermediate selectors 13 and 14 are used. The auxiliary selector 12 operates like connector 9 in accordance. with the arrangement shown in Fig. 3, z. 6., there are no means provided for automatic trunk hunting. The terminals of the auxiliary selector 12 are not connected in multiple.

If no free group selector is available, the first group selector 3 (Fig. 4) is moved to an overflow contact and causes the energization of relay 154. The relay 154 closes a guarding circuit through its right-hand high resistance winding for the trunk seized by selector 3. Upon the sending out of the impulses from the register Reg, relay 155 as- 5 sociated with the auxiliary selector 12 is ener ized, causing in turn the energization of re ay 156. Upon each energization and deenergization of relay 155 in response to the thousands digit, the selector 12 is permitted to advance its wipers through the operation of magnet 161 in the same manner as previously described in connection with the operation of connector switch 9. Following the termination of the thousands impulses relay 157 becomes energized over a circuit extending through the inner lefthand armature of relay 155, the left hand armature and contact of relay 156 and off normal contact 310, and closes a lockin circuit for itself. a

. Upon the denergization of relay 155, contact 15-is closed and therefore the circuit prepared over contact 159 of relay 154 and a slow to release relay 160 is completed. Relay 160 closes a circuit for magnet 161, 105 and relay 157 prepares a circuit for magnet 164 and auxiliary magnet 165. The circuit of magnets 164and 165 is completed upon the energization of relay 155 in response to the first impulse of the hundreds digit. The 110 setting of the selector switch 12 in response to the hundreds digit is accomplished in the same manneri as above described. Upon the seizure of a trunk, relay 166 (Fig. 4*) becomes energized, and the intermediate select- 115 ing arrangement composed of intermediate selectors l3 and 14 is actuated. Selector 13 operates like a line finder, and selector 14 hunts for a free trunk leading to a connector.

Fig. 5 is a schematic showing at an exchange in which means are provided for establishing toll connections. If no idle district or toll selector 167 is available, the group selector 168 is moved in the above described manner to a free auxiliary trunk.

By means of an intermediate switching arrangement 169, 170, an idle local group selector 171 is seized, and this selector is set under the control of a register Reg in the aeeaoce same manner as selector 168 would have been set. After the setting of the local group selector, the connection to a substation 172 associated with a distant exchange is established from 173, through 171, 168, 169, 170. 171, 175, to 172. Thus switching apparatus provided for local traffic may be used in extending a call from the group selector through an intermediate selecting arrangement 169, 170 to the connector 175, or an additional selecting apparatus may be provided in this intermediate selecting mechanism. If no idle local connector is available, means are provided for setting selector 170 on to any connector, and for applying a buzzing signal for informing an operator to sever the local connection.

Fig. 6 is a schematic representation of a system embodying the present invention and in which Strowger selectors are used. In each group of terminals controlled by the toll selector 168 an overflow or auxiliary terminal 11 is provided over which a toll connection may be established if all the regular trunks are busy. After selector 168 has been set on to this auxiliary terminal 11, a selector 169 is caused to hunt for the trunk terminating in terminal 11 which is not multipled but is individually connected to switch 169. At the same time or after the setting of the intermediate selector 169, a selector 170 is caused to select a local connector 175. The connection between exchange 173 and subscribers station 172 is established through 174, 168, 169, 170 and 175.

Fig. 7 is a schematic representation of a system embodying the present invention and in which separate connecting and talking circuits are established for the purpose of interconnecting two stations. Under the control of an operator or subscriber at exchange 176, a connecting circuit is estab lished over a non-numerical switch 177, a switching center 178, line finder 179 and a toll selector 180. The talking circuit is established from substation 181 over non-numerical switches 182, 183 (group II), toll selector 184, switching center 178, non-numerical switch 177 and toll exchange 176. If all the selectors 184 are busy, the second non-numerical switch 183 is set to select a local selector 185 over'a terminal in group III.

Then an intermediate selecting arrangement 186, 187 is selected under the control of a.

tential is connected to the b limb, a relay 191,

provided at the second non-numerical switch 183, is energized and connects ground through its front contact to the group of contacts No. II. The second non-numerical switch 183 is caused then to hunt for a free toll selector 184C. Selector 184 is then caused to select the switching center 17 8, whereupon a testing arrangement 192, 193 is energized, the talking circuit established and the connecting circuit severed. If all the toll selectors are busy, all the relays 191 are energized and their front contacts closed. Therefore, relay 195 is energized. and disconnects the ground from the b limb and connects it to the a limb. After the setting of the first nonnumerical switch 182, relay 197, associated with the second non-numerical switch 183, is energized and closes its front contact, connecting ground to the group of terminals No. III. Thus the connection will be extended to a local selector instead of to the toll selector.

At the same time relay 195, provided at the switching center, causes the operation of selectors 186, 187. 186 selects a free local talking circuit, and 187 selects the trunk leading to the switching center 17 8. If the actuated local selector 185 selects the local trunk held by switch 186, the testing mechanism 198 and 199 is actuated. Then the local selector 185 is set and the talking circuit established. Due to the fact that the local switching center remains deenergized, the local selector 186, located at the calling'side, is not operated.

What is claimed is:

1. In a telephone exchange system, a calling and a called line, means including a plurality of groups of selectively operable switching devices and trunk lines for establishing a connecting path between said lines, and means operable upon the failure of a switching device of one" group to find an available switching device of the next succeeding group of switching devices to extend the connecting path around the group of unavailable switching devices to an idle trunk normally accessible through the switching devices of said latter group.

2. In a telephone exchange system, a calling and a called line, means including a plurality of groups of selectively operable switching devices and trunk lines for establishing a connecting path between said lines, an impulse sending mechanism for controlling the operation of said switching devices and means under the control of said sending mechanism and operable upon the failure of a switching device of one group to find an available switching device of the next succeeding group of switchin devices to extend the connecting path aroun the group of un available switching devices to an idle trunk normally accessible through a switching device of said latter group. 7

3. In a telephone exchange system, a calling and a called line, means including a plurality of groups of selectively operable switching devices and trunk lines for establishing a connecting path between said lines, an impulse sending mechanism for controlling the operation of said switching devices, and auxiliary switching devices under the control of said sending mechanism and operable upon the failure of a switching device of one group to find an available switching device of the next succeeding group of switching devices to extend the connecting path around the group of unavailable switching devices to an idle trunk normally accessible through a switching device of said succeeding group.

l. In a telephone'exchange system, a calling and a called line, means including a plurality of groups of selectively operable switching devices and trunk lines for establishing a connecting path between said lines, auxiliary switching mechanism,'an impulse sending mechanism for controlling the operation of said switchin devices and said auxiliary switching mec anism, means for causing a switching device of one group to move to its overflow position upon its failure to find an available switching device of the next succeeding group of switching devices and to select an idle auxiliary mechanism and means for then operating said auxiliary mechanism for extending a connecting path around the group of unavailable switching devices to an idle trunk normally accessible through a switch of said succeeding group of switching devices.

5. In a telephone exchange system, a calling and a called line, means including a plurality of groups of selectively operable switching devices and trunk lines for establishing a connecting path between said lines, an impulse sending mechanism for controlling the operation of said switching devices, and means operable upon the failure of a switching device of one group to find an available switching device of the next succeeding group of switching devices and under the control of said sending mechanism in accordance with the digital setting of said switching devices and the digital setting of said sending mechanism formerly destined to control said unavailable switching device of said succeeding group, to extend the connecting path around the group of unavailable switching devices to an idle trunk normally accessible to a switching device of said latter group.

6. In a telephone exchange system, a calling and a called line, means including a group of first selector switches, groups of second selector switches, groups of connector switches and interconnecting trunk lines for establishing a connecting path between said lines, an impulse sending mechanism for controlling the operation of said switches, and means comprising a group of auxiliary first selector switches and a group of auxiliary second selector switches under the control of said sending mechanism and operable upon the failure of a first selector switch to find an available second selector switch of a desired group to extend the connecting path around the group of unavailable second selector switches to an idle trunk line extending to a connector switch having access to the terminal of said called line.

7 In a telephone exchange system, acalling and a called line, means including a group of first selector switches, groups of second selector switches, groups of connector switches and interconnecting trunk lines for establishing a connecting path between said lines, an impulse sendin mechanism for controlling the operation 0 said switches, means comprising auxiliary switching mechanism operable upon the failure by a first selector switch to find an available second selector switch of a desired group to extend the connecting path around the group of unavailable second selector switches to an idle trunk line extending to a connector switch having access to the terminals of said called line, and means associated with said sending mechanism for controlling said auxiliary switching mechanism in accordance with the first two digits of the designation of the desired called 110 line.

8. In a telephone exchange system, a calling and a called line, means including a first and a second selectivelyoperable switching device for interconnecting said lines, a mech- 115 anism adjustable to control the sending of two successive sets of impulses, a first and a second auxiliary switching device, means responsive to the sending of the first set of impulses for operating the first selectively op- 120 erable switching device to extend the calling line toward said second selectively operable switching device, automatic means operative thereupon for causing said first selectively operable switching device to extend the call- 125 ing line toward said first auxiliary switching device, means associated with said mechanism for causing the repeating of the first set of impulses, means responsive to the repeated sending of the first set of impulses foxcaus- 130 

